Conventional alkaline cells are typically formed of a cylindrical steel casing having a closed end and open end. The alkaline cell may typically have an anode comprising zinc and a cathode comprising manganese dioxide. The cathode active material typically comprises a mixture of particulate MnO.sub.2, graphite and KOH electrolyte solution. The anode typically comprises particulate zinc KOH electrolyte and gelling agent. The cathode material is typically in contact with the inside surface of the cell casing and the anode material is placed within the core of the casing. An ion porous separator material, typically of rayon or cellulosic material is placed between the cathode and anode. There is typically a metal pip protrusion at the end of the cell casing in electrical contact with the cell casing and cathode. The pip protrusion typically forms the cell's positive terminal. After the cell is loaded with anode, cathode, separator, and electrolyte, the open end of the casing is sealed with an end cap assembly which may include an insulating member, metal end cap and elongated current collector. The end cap is in electrical contact with the anode material through the current collector and typically forms the cell's negative terminal.
The pip protrusion (positive terminal) in electrical contact with the cell casing is typically formed by a separate plate having a pip protrusion emanating therefrom. Such plate is welded to the flat bottom of the casing, that is at the casing's closed end. The welding of the plate to the cell casing causes the pip protrusion to be in electrical contact with the casing and form the cell's positive terminal. The method of forming the positive pip protrusion by welding a separate plate to the flat bottom of the cell's casing has the disadvantage that it requires a separate processing step and also additional material.
Alternatively, the pip protrusion may be formed during the deep draw ing process used in fabricating the cell casing. Cylindrical cell casings for alkaline cells are conventionally fabricated by the deep drawing method wherein the diameter of the casing is progressively reduced in a series of steps employing punches each having a smaller diameter than the one preceding. The pip protrusion may be formed during the latter stages of this process but at the expense of additional tooling required to form the pip protrusion mold on at least several punches, each of progressively smaller diameter. Such punches wear out frequently and have to be replaced. Additionally, the pip protrusion formed on the casing may subsequently be damaged during transport and handling. The process of compacting cathode material into the can having a preformed pip protrusion may also cause distortion of the pip. Alternatively, the pip protrusion may be formed in a separate step after a flat bottom cylindrical casing has been formed. Thus, a plunger or mandrel may be pushed into the casing interior causing the casing closed end (flat bottom) to be pushed out at its center to form the desired pip protrusion before the casing is loaded with active materials. The method of forming a pip protrusion in this manner, has the disadvantage that it requires a separate processing step, additional equipment and the added expense and assembly time associated with such processing.
It is thus desirable to form the positive pip protrusion for an alkaline cell in a manner that will eliminate the need for additional materials and separate processing steps so that the overall cell assembly time may be reduced.